Pacemakers are medical instruments designed to help regulate abnormal heart rate and rhythms by sending electrical pulses to the heart, causing it to contract and pump blood. In addition to an initial implant surgery, they require several additional surgeries to replace their batteries. Due to limited battery life, another open-heart surgery must be conducted to replace the pacemaker, risking the life of the patient with the threat of infection, blood loss, heart attack, or stroke . Piezoelectric nanogenerators with Zinc Oxide nanowires can be used as an alternative to pacemakers, utilizing the body’s own kinetic energy as a power source .
Piezoelectric materials are a class of solids that produce an electrical potential (or voltage) when subjected to mechanical stress (squeezing, bending, etc.) . The human body is full of piezoelectric energy sources such as muscle movement, vibrational energy from the larynx (or voicebox), and hydraulic energy from blood and other bodily fluids. Nanogenerators utilizing piezoelectric materials are made of a conductive substrate from which the Zinc Oxide nanowires extend, flexing to touch a silicon electrode when stimulated by mechanical stress. The current generated by the movement of the nanowires is stored in a zinc oxide coating on the substrate, and then transferred through the Zinc Oxide nanowires (platinum-tipped for enhanced conductivity) into the silicon electrode, which then powers the implanted pacemaker .
The electricity produced, however, is of a small magnitude—in the nano-Ampere, or one billionth of an amp, range. Though this amount of current is not suitable for conventional sized batteries, it may be applied to nanoscale devices. Piezoelectric nanogenerators have the potential to revolutionize biomedical devices by utilizing the human body as an energy source, increasing the longevity of the technology . Through this, healthcare costs are reduced, the need for multiple surgeries is eliminated, and energy is produced cleanly and sustainably.
A piezoelectric nanogenerator at the Center for Mechanics and Materials and Department of Engineering Mechanics, Tsinghua University.
(Source: Thorac, 2014)
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Piezoelectric nanogenerators are the first appropriate power sources for nanoscale devices, as the batteries needed to power nanoscale devices are often larger than the nanotechnology itself. As the power source is derived from kinetic energy produced by the body, pacemakers equipped with this technology are more sustainable and have a longer lifespan uninhibited by a conventional battery.
Powering nanoscale devices has always been a tremendous engineering challenge. If conventional batteries or powering methods were used, the size of the power source would likely nullify any size advantages offered by nanoscale devices. Furthermore, traditional batteries tend to use chemicals that would be toxic to the body. Zinc oxide nanowires, which are biocompatible, enable the piezoelectric nanogenerators to be safely incorporated into the body. Zinc oxide nanowire nanogenerators can also be packaged inside polymers to prevent the risk of short-circuiting when exposed to biofluids . This technology will ultimately decrease the number of surgeries needed by a pacemaker, allowing more freedom to the consumer.
While implanted nanogenerators have been successfully tested in lab rats; human trials have not yet been conducted. Risks associated with the implementation and biocompatibility of Zinc oxide nanowire nanogenerators are still unknown until additional research can be conducted. In addition to the unknown health risks, the use of a Zinc Oxide nanowire array is potentially hazardous due to the highly flammable nature of phosphorus. Malfunction of the device poses a significant threat to a critical organ system and would require invasive surgery to correct.